The proposed research may be considered in four areas: 1) Having shown that macro-molecular intestinal transport is inhibited more effectively by oral immunization than by parenteral immunization because of the differences in specific immunoglobulins produced locally in these two methods of immunization, class specific antibodies (IgGa, IgGl, and IgM) to bovine serum albumin (BSA) and to horseradish peroxidase (HRP) will be separated and complexed at equivalence for study. Antigen complexes and antigens alone will be compared as to adsorption to brush border membranes and uptake into epithelial cells both physiologically and morphologically (using enzyme-antibody conjugation to identify macromolecules ultrastructurally). Results can be used to determine the antibody class involved in decreased uptake and to localize the site of antibody interference with antigen absorption. 2) Antigens are taken up by a pinocytotic mechanism requiring first cellular binding and then invagination. The characteristics of binding of I125-HRP and I125-BSA antigens to purified brush border membranes will be determined with regard to energy requirements, competitive inhibition, enhancement with charged polypeptides and effect of immunization (secretory and systemic antibodies). 3) Data from above studies will be applied to the study of physiologic macromolecules (bacterial enterotoxins such as cholera toxin and food proteins). Normal brush border binding and uptake characteristics will be noted morphologically using HRP-conjugated antibodies and compared to immunized animals. Uptake in control and immunized animals will be determined using radiolabeling techniques. 4) In vivo studies using the rat lymph fistula model will be done to confirm in vitro binding and uptake studies with and without immunization.